US2342169A

US2342169A - Quartz crystal oscillator

Info

Publication number: US2342169A
Application number: US441585A
Authority: US
Inventors: George T Royden
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC; Federal Telephone and Radio Corp
Priority date: 1942-05-04
Filing date: 1942-05-04
Publication date: 1944-02-22
Anticipated expiration: 1961-02-22

Description

Feb. 22; 1944.

e. T. ROYDEN QUARTZ CRYSTAL OSCILLATOR Filed May 4;"1942 I I'EEQUE/VC Y INVENTOR 6. TRog'ae/I ATTORNEY Patented Feb. 22, 1944 QUARTZ CRYSTAL OSCILLATOR George T. Royden, South Orange, N..J.,

assignor Federal Telephone and Radio Corporation,

a corporation of Delaware Application May 4, 1942, Serial Ne. 441,585

16. Claims.

This invention relates to electron tube oscillator generators and more especially to such generators provided with a crystal type frequency stabilizer.

A principal object of the invention relates to a crystal stabilized oscillator generator wherein the stabilization effect of the crystal is substantially equalized for both positiverand negative departures of the oscillator from a standard frequency.

Another principal object is to provide a vacuum tube oscillator generator which is to be stabilized by a quartz crystal and wherein a duplex comparison network is provided for comparing the resonant frequency of the crystal with the generated frequency of the oscillator, one of said networks being effective for a positive departure and the other being effective for a negative departure of the generator from a standard frequency.

Another object is to provide the frequencydetermining circuit of an electron tube oscillator generator with a pair of grid-controlled tubes which are selectively effective on the frequencydetermining circuit under control of, and in accordance with, the direction of departure of the generated oscillations from the resonant frequency of the crystal.

A feature of the invention relates to an electron-tube oscillator generator whose tank circuit feeds a triple branched frequency stabilizing network, one branch comprising mainly inductive reactance, another branch comprising mainly capacity reactance, and the third branch comprising mainly the reactance of the crystal, said branches being connected to an electron tube network which produces a pair of independent electron streams selectively effective to control the frequency of the generated oscillations in accordance with the phase relation of the voltage in said crystal branch compared with the voltages in the said other two branches.

Another feature relates to an electron-tube oscillator generator having a tank circuit shunted in part by a variable impedance which controls the generated frequency, the value of said impedance being determined by a pair of independent electron discharge paths which are in turn selectively effective in accordance with the amount and phase of departure of the generated frequency from the resonant frequency of the crystal.

Another feature relates to an oscillator generator and a crystal frequency stabilizer therefor, including a pair of multi-grid electron tubes having their control grids excited in phase with a voltage derived from the tank circuit of the oscillator and in phase with the excitation of the crystal, each of said tubes having another impedance-controlling grid the relative phases of excitation of which are determined by the departure of the generated frequency from the resonant frequency of the crystal.

A further feature relates to a crystal stabilized network for electron tube oscillators comprising a balanced triple-branched network, one branch comprising mainly a capacity reactance, the second branch comprising mainly an inductive reactance and the third branch comprising the reactance of the crystal, each of said branches including .a balancing resistance whereby the voltage developed across the capacity and inductance 'reactances aresubstantially equal when the generated frequency is substantiallythe same .as the crystal resonant frequency, said voltages determining respectively the impedance of a corresponding pair of grid-controlled electron tubes which in turn selectively determine the automatic tuning of the tank circuit of the generator.

A further feature relates to an electron tube oscillator generator having a tank circuit with a variable-impedance electron tube as a tuning control element, and a double rectifier arrangement connected to the control grid of said tube for determining the conductivity thereof, the conductivity of the sections of said rectifier being selectively controlled by a three-branch network having a capacity arm, an.inductance arm and a crystal reactance arm.

A still further feature relates to the novel interconnection of parts which cooperate to produce a highly efiicient and accurate frequency stabilizer for electron tube generators.

Other features and advantages not particularly enumerated will reveal themselves upon consideration of the ensuing description and claims.

While the invention will. be disclosed in connection with certain specific forms of tubes and related apparatus, this is done merely to explain the inventive concept and not by way of limitation. In the drawing,

Fig. l is a schematic circuit diagram of one embodiment of the invention.

Fig. 2 is a modified embodiment of the invention..

Figs. 3 and 4 are respectively an explanatory curve and vector diagram relating to the embodiment of Fig. 2.

Referring to Fig. l, the thermionic vacuum tubes I, 2, 3 and 4 are furnished heater current from battery 5 and plate and screen current from battery 6. The oscillator tube I has a resistor and capacitor 8 in its cathode circuit and resistor 9 and capacitor Ill in its screen circuit. Plate current is obtained through choke coil The oscillator tank circuit contains an inductor l2 and a capacitor I3; These are connected to the grid, cathode (through capacitor 8) and anode (through blocking capacitor l4) of the oscillator tube l as shown in Fig. 1.

A portion of the oscillator tank circuit is shunted (in effect) by inductor l5 and vacuum tube 2, the effective amount of reactance contributed to the oscillator tank circuit being controlled by the grid and screen voltages of vacuum tube 2. These voltages are in turn controlled by the currents passing through vacuum tubes 4 and 3 respectively.

. 'The radio frequency potential existing in the oscillator tank circuit (at the end connected to the-anode) is impressed through resistors l6, I1 and I8 on an inductor I9. a quartz crystal 2D and a capacitor 2| respectively. The potential drop across the quartz crystal 20 is impressed on the grids of vacuum tubes 3 and 4. This potential will be small and in phase with the oscillator tank circuit voltage if the frequency of the oscillator is equal to the resonance frequency of the quartz crystal. The resistance of resistor I1 is chosen so; that it is large compared with the equivalent series resistance of the quartz crystal at resonance. The voltage across the quartz crystal will lead in phase the voltage from the oscillator tank circuit for frequencies above the resonance frequency of the quartz crystal and lag in phase for frequencies below resonance. The magnitudes of resistor l6 and inductor l9 are such that the voltage across inductor I9 is substantially leading in phase with respect to the oscillator tank circuit voltage. Capacitor 22 serves to prevent screen current passing through inductor 9 thus preserving balance with respect to vacuum tube 4. The magnitudes of resistor I8 and capacitor 2| are such that the voltage across capacitor 2| is substantially lagging in phase with respect to the oscillator tank circuit voltage. The magnitudes of l6, l8, l9 and 2| are such that the voltage across capacitor 2| is substantially the same as that across inductor l9. Furthermore, resistors .23 and 24 are substantially equal also

resistors

25 and 26 and capacitors 21 and 28 in order to preserve balance between the circuits containing vacuum tubes 3 and 4. prevent rapid changes .in plate potential of vacuum tubes 3 and 4. 4

If the frequency of the vacuum tube oscillator is above the resonant frequency of the quartz crystal 20, the grid voltage of vacuum tube 3 will be leading (with respect to the oscillator tank circuit) and substantially in phase with the screen voltage. Since these potentials are normally near the cut-off point of the vacuum tube characteristic (point at which plate current drops to zero), only the positive portion of the radio frequency cycle permits plate current to flow. An increase of plate current in vacuum tube 3 results in a greater voltage drop in resistor 23 and consequently a drop in screen voltage of the reactance control vacuum tube 2. This decreases the effectiveness or coupling of the inductor Hi to the oscillator tank circuit thereby lowering the frequency of oscillation. r

If the frequency of oscillation of the

vacuum Capacitors

29 and 3|! tube oscillator is below the frequency of resonance of the quartz crystal 20, the grid voltage of vacuum tube 4 will be lagging (with respect to the oscillator tank circuit) and substantially in phase with the screen voltage. Vacuum tube 4 will then pass current which raises the potential applied to the grid of the reactance control tube 2. Such a change in impedance of vacuum tube 2 increases the coupling of inductor |5 to the vacuum tube oscillator tank circuit and raises its frequency of oscillation.

Thus it will be seen that frequency of oscillation will automatically be corrected until it coincides with the frequency of resonance of the quartz crystal.

Referring to Fig. 2, there is shown a simplified embodiment of the invention wherein the vacuum tubes 3 I, 32 and 33 are furnished filament current from battery 34. Plate current is supplied to vacuum tubes 3| and 32 by battery 35 through a radio frequency choke coil 36. An oscillating tank circuit comprising inductor'3! and capacitor 38 is connected to the cathode (via a tap on the coil 31) to the grid and to the anode, via blocking capacitor 39, of vacuum tube 3|.

Energy from-the oscillating tank circuit is applied through resistors 40, 4| and 42 to capacitor 43, quartz crystal 44 and inductor 45 respectively, returning to ground and the oscillating tank circuit. Crystal 44 connects directly with ground, while capacitor 43 and inductor 45 have their connection to ground through capacitor 46 which is of such capacitance that the voltage drop across it for the radio frequency currents that flow is negligible. i

The voltage drop across capacitor 43 is applied to one plate of the dual rectifier tube 33. The voltage drop across inductor 45 is applied to the cathode of the other rectifier unit of vacuum tube 33. The voltage drop across the quartz crystal 44 is applied to the cathode and anode not previously mentioned.

Referring to Fig. 3, the voltage drop across the capacitor 43 is shown by the line A, that across the inductor 45 by the line B and thatacross the quartz crystal by the line C.

Referring to Fig. 4, the relative phase and approximate magnitude of these'voltage drops are shown. The voltage obtained from the oscillating tank circuit is assumed to be vertical and several times larger than any vector shown. The voltage drop across the capacitor 43 is indicated as a, and that across inductor 45 by vector 6. These are for a frequency near the desired frequency of oscillation but, as may be readily seen from later discussion, have little effect on the stability of the system. Vector 0 shows the voltage drop across the quartz crystal when the ap plied frequency is near the resonant point of the crystal. Vector a shows this voltage drop for a frequency above the resonant frequency of the quartz crystal 44 and vector e for a frequency below the resonant frequency. 1

The resonant frequency of the oscillator tank circuit is chosen slightly below the desiredfrequency (resonant frequency of the quartzcrystal) and the inductor 41 so chosen that, when it is shunted across'a portion of the oscillator tank circuit, the frequency will be above the desired frequency. Furthermore, the coupling be tween the inductor 41 and the oscillator tank circuit by means of the vacuum tube 32 is of the amount necessary to bring frequency of oscillation to the desired frequencywhentheva'c uum tube 32 is at a point-on its operatingchai' acteristic near the center of its: normal range of operation.

If the oscillation frequency is above the resonant frequency'of the quartz crystal 44, the difference between vectors 2) and (I will be much smaller than the difference between vectors a and (1. Therefore, more current will be rectified by the rectifier unit shown at the right than the unit at the left, and the voltage across capacitor 46 will become more negative with respect to ground. This reduces. the grid voltage of the reactance control tube 32 thereby reducing the coupling between inductor 41 and the oscillator tank circuit which reduces the frequency of oscillation.

If the oscillation frequency is below the resonant frequency of the quartz crystal, the difference between vectors a and e will be small in comparison with the difference between 'vectom 2) and e. Therefore, more current will be rectified by the rectifierunit at the left than by the unit at the right, and the capacitor 46 will be charged positively. This increases the grid voltage of the reactance control tube 32 thereby increasing the coupling between inductor 41 and the oscillator tank circuit, consequently increasing the frequency of oscillation. Radio frequency choke coil 48 serves to. conduct rectified current around the capacitor 43. This is necessary to preserve symmetry and balance of the circuits associated with the two rectifiers. Thus it may be seen that the frequency of oscillation will be automatically corrected to coincide with the resonant frequency of the quartz crystal.

The design of the circuit described above may be made so that the oscillator may be frequency modulated by any of the well-known methods and the average frequency automatically corrected to coincide with the resonant frequency of the quartz crystal through the rectifying action of the rectifier units and integration of the rectified currents in the capacitor 46.

It is obvious to one skilled in the art, that the vacuum tubes 3! and 32, which are shown as separate triodes, may be two triodesin a common envelope or may be pentodes or combinations of a triode and a pentode and may be in a common or in separate envelopes. Furthermore, the system described may be used with the diode rectifiers in separate envelopes.

What I claim is:

l. A system for stabilizing the frequency of an oscillator generator having a variable frequencydetermining element and, a crystal stabilizer therefor, which comprises means to develop in separate paths two voltages which lag and lead respectively the phase of generator voltage by predetermined amounts when the generator frequency is substantially the same as the resonant crystal frequency, means to excite the crystal in phase with the generator voltage, means to compare the relative. phases between the .crystal voltage and said two voltages, and means automatically responsive to -said comparison to maintain the generator frequency at said resonant crystal frequency.

2. A system for stabilizing the frequency of an oscillator generator having a variable frequencydetermining element and a crystal stabilizer therefor, whichcomprises means to excite the crystal substantially in phase with the generator Voltage, means to develop in two separate paths under control of the generator voltage two voltages which are substantially equal in magnitude but which respectively lead and lag the generator voltage bypredetermined amounts. when thegenerator frequency is substantially the same as the resonant crystal frequency, meansto. develop a frequency correction voltage which is a function of the phase differences of said two voltages with respect to the crystal voltage, and means to applysaid correction voltage'to control the effectiveness of said frequency determining element.

3. A system according to claim 2 in which the means to develop said correction voltage includes a pair of electron streams between corresponding pairs of cathodes and anodes with a pair of grids in each stream one grid ofeach pair being excited in phase with the crystal excitation the other grids of each pair being excited respectively by said two voltages.

4. A system according to claim 2 in which the means to develop said correction voltage includes a pair of multi-grid electron tubes each having a first grid and a second grid the first grid of each tube being excited in phase with the excitation of the crystal and the second grid ofeach tube being excited respectively by one of said two voltages.

5. A system according to claim 2 in which the means to develop said correction Voltage includes a pair of multi-grid electron tubes of the shield grid type the control grids of the tubes being excited in phase with the excitation of the crystal and the shield grids being each excited respectively by one of said two voltages.

I 6. A system according to claim 2 in which the meansto develop said correction voltage includes a pair of pentode tubes with their suppressor grids connected to their cathodes, with the control grids excited in phase with the excitation of the crystal and the shield grids each excited respectively by one of said two voltages.

7. A system according to claim 2 in which the means to. develop said correction voltage includes a double rectifier one section of which is controlled by the voltage diiference between the crystal voltage and one of said two voltages, and the other section of which is controlled by the voltage difference between the crystal voltage and the other of said two voltages.

8. A system for stabilizing the frequency of an electron tube oscillation generator having a frequency-determining element connected to a tank circuit and whose effectiveness is controlled by a variable impedance grid-controlled electron tube, which comprises three voltage paths the first being predominantly capacitive, the second being predominantly inductive, and the third including a frequency stabilizing crystal, means to apply to said paths a voltage of the generator frequency and derived from the tank circuit, means to adjust the phase of each path so that when the generator frequency is substantially the same as the resonant crystal frequency the phase differences between the crystal path and the other two paths is ineffective to vary the impedance of said variable impedance tube, and means effective when the generator frequency departs from the r resonant crystal frequency and controlled by the relative phase differences between said two paths and the crystal path to apply a voltage to the control grid of said variable impedance tube to restore the generator frequency to that of the resonant crystal frequency.

9. A system according to claim 8 in which the crystal path is excited in phase with the generator voltage.

10. A system according to claim 8 in which the voltages developed in said two other paths are substantially the same magnitude when the generator frequency is the same as the resonant crystal frequency.

' 1 1. A system for stabilizing the frequency of an electron tube oscillation generator, comprising a pair of grid-controlled tubes, three paths excited from the tank circuit of the generator, the first path including a crystal stabilizer, the second path having a leading characteristic with relation to the crystal path, and the third path having a lagging characteristic with relation to the crystal path, means to connect said three paths to both said grid-controlled tubes so that the plate current of one tube'is a function of the phase difierence between the first path and the crystal, and the plate current of the other tube is a function of the phase difierence between the third path and the crystal path, and means to develop a frequency correction voltage which is a resultant of the plate currents of said pair of tubes.

12. A system for stabilizing the frequency of an electron tube oscillator generator, comprising three paths connected to the tank circuit of the generator, one of said paths having a resonant crystal voltage-frequency characteristic curve, the second of said paths having a falling characteristic curve with the voltage drop across the path falling as the frequency is increased, the third of said paths having a rising characteristic curve with the voltage drop across the path rising as the frequency is increased, means to adjust the impedances of each path so that when the resonant crystal frequency is substantially the same as the generator frequency the point of insection of the characteristic curves of the second and third paths is located substantially at the resonant frequency of the crystal, and means to develop a frequency correction voltage for the generator which is a function of the resultant of the differences between the voltages in said second and third paths with respect to the voltage in the crystal path.

13. A system according to claim 12 in which the last-mentioned means comprises a rectifier having two sections, the said first path being connected between the cathode of one rectifier section and ground, the second path being connected between the anode of said one rectifier section and ground, the third path being connected between the cathode of the other rectifier section and ground, said crystal path being also connected to the anode of said other rectifier section.

14. A system for stabilizing the frequency of an electron tube oscillator generator, comprising a rectifier having two sections, a. network having a falling voltage-frequency characteristic and connected to the anode of one rectifier section. another network having a rising voltage-frequency characteristic and connected to the cathode of the other rectifier section, a stabilizing crystal connected to the cathode of the first section and to the anode of the second section, a grid-controlled variable impedance tube, and means to apply to the grid of said tube a voltage which is the resultant of the currents in said two rectifier sections, and means to connect said gridcontrolled tube to the tank circuit of the generator so that variations in impedance of said tube result in variations of the generator frequency.

15. A system according to claim 14 in which means are provided to adjust the impedance in each of said paths so that said resultant is of a fixed predetermined magnitude when the generator frequency is substantially the same as the resonant crystal frequency.

16. A frequency stabilizing system for an electron tube oscillator generator having a tuned tank circuit controllable by a reactance connected to a grid-controlled variable impedance tube, which comprises a pair of grid-controlled tubes for selectively controlling the magnitude of the plate current of said impedance tube, a triple branch network for selectively controlling the plate current of said pair of tubes one branch comprising an inductive reactance connected to an impedance regulating grid of one of said pair of tubes, a second branch comprising a capacitive reactance connected to an impedance regulating grid of the other of said pair of tubes, the third branch including a crystal reactance connected to the control grids of both said pair of-tubes, said three branches being excited from said tank circuit. GEORGE T. ROYDEN.